Mercury was first visited by the Mariner 10 probe, in January 1974, the probe was originally designated to study both Venus and Mercury but after the Soviet surprised the world with a manned flyby of Venus. The United States decided to use the probe as a pathfinder and a technology demonstrator for a manned flyby of both these worlds to keep up with the Soviets in the early years of the Space Race.
The manned mission followed closely behind and while the probe made quick flyby of Mercury the American mission was able to orbit briefly and deliver a scientific payload to the surface. Several other American and Soviet orbital missions would continue over the next several years with the American landing three times.
In 1993, Japan became the second nation to land on Mercury. The Japanese set up a small temporary base in the hopes of finding "Rare Earths," which are needed in the electronics and differcult to get on earth as the largest resources are in war-torn China.
Takao Doi was the first Japanese astronaut to land on Mercury and his mission found enough evidence of a deposit of Neodymium (used in advanced magnets) to warrent further investagation. With the discovery of Neodymium, it was hoped other rare elements may also be common, as the supplys of these elements are in short supply and are slow coming out of China which has the largest supplies.
With thge discovery of these rare earths, the United States and Japan started to build a joint base to further explore Mercury. In 1995, Cliffs Natural Resources a large American mining company open a mining operation.